1. Field of the Invention
The present invention relates to a golf club head.
2. Description of the Related Art
In general, a plurality of parallel linear grooves are formed in the face surface of a golf club head to extend in the toe-to-heel direction (for example, Japanese Patent Laid-Open Nos. 9-84909 and 2007-202633). These grooves are called, for example, scorelines, marking lines, or face lines (they will be referred to as scorelines in this specification). These scorelines have an effect of increasing the back spin amount on a struck golf ball, or suppressing a significant decrease in back spin amount on a struck golf ball upon a shot in rainy weather or that from the rough. To adjust the spin amount on a struck golf ball, a technique of forming grooves different from the scorelines in the face surface (for example, Japanese Patent Laid-Open No. 2007-202633), and a technique of forming a plurality of types of grooves in the face surface (for example, Japanese Patent Laid-Open No. 2010-35846) have also been proposed.
A rule concerning the scorelines of an athletic golf club head stipulates that the edge of each scoreline must fall within a virtual circle which has a radius of 0.011 inches and is concentric with a virtual circle which has a radius of 0.010 inches and is inscribed in both the side wall of this scoreline and the face surface. To comply with this rule, it is possible to form rounded portions on the edges of the scorelines.
On the other hand, the scorelines serve as indices for matching the orientation of the face surface with the target direction upon address. When the edges of the scorelines are chamfered, the boundaries between the scorelines and the face surface often become visually obscure. If the scorelines are hard to see upon address, it is difficult to match the orientation of the face surface with the target direction. To improve the visibility of the scorelines, it is possible to color the scorelines. However, when a colorant is used to coat the scorelines, the coating material may peel off or degrade the spin performance of a golf ball.